Product terms in PLDs — which gate produces them? Inside a PAL/GAL/CPLD logic array that implements sum-of-products, the signals known as “product terms” are the outputs of what kind of gate?

Introduction / Context:
Programmable logic devices often realize Boolean functions using the sum-of-products form. In this style, “product terms” and “sum terms” refer to intermediate signals inside the logic plane. Knowing which gates generate these signals clarifies how equations map onto hardware resources like macrocells and product term allocators.

Given Data / Assumptions:

• Sum-of-products means OR of ANDs (e.g., F = AB + CD).
• PLDs feature a programmable AND plane followed by an OR function per output macrocell.
• Signals may be available in both true and complemented forms to the AND plane.

Concept / Approach:
Each “product term” corresponds to the logical product (AND) of a selected set of literals (variable or its complement). The programmable connections into the AND plane define which literals are included. The outputs of these AND gates are then ORed to form the final logic equation for a given macrocell output.

Step-by-Step Reasoning:

Verification / Alternative check:
Block diagrams of PAL/GAL devices label the first stage as a programmable AND array producing product terms, confirming the terminology used in textbooks and datasheets.

Why Other Options Are Wrong:

• OR/XOR/NOR: these are used elsewhere (summing, polarity), not for forming product terms.
• Flip-flop: sequential storage, not combinational product generation.

Common Pitfalls:

• Confusing “product term” with “sum term”; sum terms arise from ORing product terms.

Final Answer:
AND